disk: fix composite disk component path handling.
disk: fix composite disk component path handling.

Currently we treat any version 1 path as absolute, and any non version 1
path as relative. The proto files don't indicate that this assumption
can be made, and we don't make it on Windows. This CL changes path
handling so that a version 1 path must actually be absolute for us to
treat it as such.

TEST=builds
BUG=b:213150316

Change-Id: I95a1c8751428a9e2f7311f9136940fbdb2410ef1
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/3654207
Reviewed-by: Daniel Verkamp <72bc170b46ec491f7bdd4359a1c0bfed274de40c@chromium.org>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Commit-Queue: Noah Gold <2d4550d8af93bfc6e6fbe1fb1b0cc97a9ee7c3ce@google.com>

google/crosvm,google/crosvm,google/crosvm,google/crosvm